I. Field of the Disclosure
The technology of the disclosure relates to three-dimensional integrated circuits (3DICs).
II. Background
Mobile communication devices have become common in current society. The prevalence of these mobile devices is driven in part by the many functions that are now enabled on such devices. Demand for such functions increases processing capability requirements and generates a need for more powerful batteries. Within the limited space of the housing of the mobile communication device, batteries compete with the processing circuitry. These and other factors contribute to a continued miniaturization of components and power consumption within the circuitry.
Miniaturization of the components impacts all aspects of the processing circuitry including the transistors and other reactive elements in the processing circuitry. One miniaturization technique involves arranging integrated circuits in not just an x-y coordinate system, but also in a z-coordinate system. That is, current miniaturization techniques use three-dimensional (3D) integrated circuits (ICs) (3DICs) to achieve higher device packing density, lower interconnect delay, and lower costs. Currently, there are several techniques to manufacture or form 3DICs.
A first technique to form a 3DIC is selective epitaxial layer growth. Selective epitaxial layer growth can produce acceptably decent quality ICs, but this technique is expensive due to the rigorous requirements associated with the process. A second technique to form a 3DIC is a wafer-on-wafer manufacturing technique, whereby electronic components are built on two or more semiconductor wafers separately. The two or more semiconductor wafers are stacked, aligned, bonded, and diced into 3DICs. Through silicon vias (TSVs) are required and provided to effectuate electrical connections between the stacked wafers. Misalignment or TSV defects in any of the stacked wafers can result in an entirely defective integrated circuit due to the interdependence of the IC on the various layers. A third technique to form a 3DIC is a die-on-wafer technique, whereby electronic components are built on two semiconductor wafers. In this technique, one wafer is sliced and the singulated dice are aligned and bonded onto die sites of the second wafer. This die-on-wafer technique can also suffer from alignment issues. A fourth technique to form a 3DIC is a die-on-die technique whereby electronic components are built on multiple dice and then stacked, aligned, and bonded. This approach suffers from the same misalignment problem which may render the final 3DIC unusable.
A fifth technique to form a 3DIC is a monolithic technique, whereby electronic components and their connections are built in layers on a single semiconductor wafer. The layers are assembled through an ion-cutting process. The use of the layers in this fashion eliminates the need for precise alignment and TSVs. In the monolithic approach, a receptor wafer is prepared with integrated components thereon. An oxide layer forms on a top surface of the receptor wafer. A donor wafer is prepared by subjecting the donor wafer to an ion (typically hydrogen) implantation process. The surface of the donor wafer with the ion implantation is then stacked onto the oxide layer of the receptor wafer. The oxide layer of the receptor wafer bonds with the surface of the donor wafer through an annealing process. The donor wafer is then removed, transferring a silicon layer to the receptor wafer. Additional electronic components and interconnects are fabricated over the transfer silicon layer sequentially. The monolithic approach is less expensive than epitaxial growth and eliminates the risk of misalignment, resulting in more functional devices than the techniques that rely on wafer-to-wafer, wafer-to-die, or die-to-die alignment.
The monolithic approach makes integrated circuits with small footprints, but the density of active components in the three-dimensional integrated circuit generates relatively greater amounts of heat than a simple two-dimensional integrated circuit. High temperatures can negatively impact performance of the active components in the circuit. Further, by arranging the circuit in three dimensions instead of just two dimensions, new opportunities for electromagnetic interference (EMI) or crosstalk between circuits are also created. EMI also negatively impacts performance of the active components in the circuit.